Solid-state imaging systems or imaging readers have been used, in both handheld and/or hands-free modes of operation, in supermarkets, warehouse clubs, department stores, and other kinds of retailers and other businesses for many years, to electro-optically read, by image capture, targets, such as one- and/or two-dimensional bar code symbols, each bearing elements, e.g., bars and spaces, of different widths and reflectivities, to be decoded, as well as other targets or forms, such as documents, labels, receipts, signatures, drivers' licenses, employee badges, payment/loyalty cards, and the like, each form bearing alphanumeric characters and/or graphics and/or symbols, to be imaged and processed.
A known exemplary imaging reader includes a housing held by a user, a window supported by the housing and aimed at the target by the user, and a scan engine or imaging module supported by the housing and having a solid-state imager (or image sensor) with a sensor array of photocells or light sensors (also known as pixels), and an imaging lens assembly for capturing return light scattered and/or reflected from the target being imaged along an imaging axis through the window over an imaging field of view, and for projecting the return light onto the sensor array to initiate capture of an image of the target over a range of working distances in which the target can be read. Such an imager may include a one- or two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device and associated circuits for producing and processing electrical signals corresponding to a one- or two-dimensional array of pixel data over the field of view. These electrical signals are decoded and/or processed by a programmed microprocessor or controller into information related to the target being read, e.g., decoded data indicative of a symbol, or into a picture indicative of a form. In the handheld mode of operation, the user holds the housing in his or her hand at a certain working distance from the target to be imaged, aims the window at the target, and manually activates a trigger on the housing to initiate a reading session.
In order to increase the amount of the return light captured by the imager, especially in dimly lit environments and/or at far range reading, the imaging module generally also includes an illuminating light assembly for illuminating the target with illumination light for reflection and scattering therefrom. The illumination light preferably is distributed along an illumination pattern over and along the target. The distributed illumination pattern is typically generated by using a pair of spaced-apart light emitting diodes (LEDs) and a pair of cylindrical lenses.
Since the user of the imaging reader cannot see exactly whether a target is located entirely within the imaging field of view of the imager, or know whether the target is optimally centrally located within the imaging field of view, the imaging module also typically includes an aiming light assembly for projecting a visible aiming light pattern, for example, a generally circular spot, or a cross-hairs, for placement at or near the center of the target, or an aiming line, or a series of generally circular spots linearly spaced apart, for placement lengthwise along the target, to assist the user in visually locating the target within the imaging field of view and, thus, advise the user in which direction the housing is to be moved in order to accurately position the aiming light pattern on the target prior to reading. The aiming light assembly includes an aiming light source, such as one or more LEDs and aiming lenses, or a laser and a pattern shaping optical element, such as a diffractive optical element (DOE), or a refractive optical element (ROE). The focused light passing through a respective DOE forms multiple diverging beamlets, which project continuous lines or rows of spots arrayed in the aiming light pattern on the target to indicate the imaging field of view.
Such known imaging readers are often operated to read symbol targets on picklists. A picklist is typically a document or a display screen on which many symbol targets are printed or displayed, each symbol target corresponding to an item to be managed. The items can identify physical items, such as food, materials, equipment, component parts, and like products in inventory, as well as abstract items, such as time, information, equipment settings, and the like. Such items are managed in many fields, such as material handling, production, packaging, inventory, transportation, warehousing, information flow, and security, just to name a few. The imaging reader is operated to read a selected symbol target from the many symbol targets on the picklist, thereby automatically identifying the corresponding item to a remote host computer for further processing and management.
Although the known imaging readers are generally sufficient for their intended purpose, they have sometimes proven to be less than satisfactory when operated to read symbol targets on the picklist. The symbol targets are generally printed or displayed closely adjacent one another on the picklist. The imaging field of view of the imaging reader diverges outwardly of the imaging reader over the range of working distances relative to the housing. The diverging imaging field of view often contains more than one symbol target, and this effect is exacerbated as the working distance between the target and the housing increases, with a concomitant increase in the size of the diverging imaging field of view. It is therefore often difficult to read just the one particular symbol target that is desired, especially at the far end of the range.
The art has addressed this issue by employing a picklist mode of operation, wherein two types of images of the picklist are captured each time that a symbol target is to be read. At least one image of the first type is captured with the aiming light pattern on the selected symbol target, i.e., with the aiming light assembly energized; and at least one image of the second type is captured without the aiming light pattern, i.e., with the aiming light assembly deenergized. The controller determines from the image of the first type which symbol target was the one selected, i.e., the one on which the aiming light pattern was present, and then, now knowing the location of the selected symbol target from the image of the first type, the controller only processes the selected symbol target from its determined location in the image of the second type.
While the number of images of the first type and the number of images of the second type may vary in each reading session, which starts from the time of trigger activation and ends with either a successful decode or a failed attempt to decode, there are generally at least one image of the first type and at least one image of the second type acquired, in the picklist mode of operation. Although the picklist mode of operation sometimes fails, decoding and reading of the selected symbol target are always delayed, thereby causing the reading performance of the imaging reader to sometimes be perceived as sluggish by the user. Having to take at least two different types of images of the picklist each and every time that a symbol target is to be read also imposes a processing burden on the controller.
Accordingly, there is a need to provide an apparatus for, and a method of, electro-optically reading a selected target, by image capture, from a picklist of targets contained in an imaging field of view, without having to take at least two different types of images of the picklist each and every time that a symbol target is to be read, and to render the reading performance more aggressive, and to ease the processing burden on the controller.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.